The present invention relates to a magnetoresistive read-write head of the type used for a magnetic recorder; and, more particularly, the invention relates to a read-write head incorporating a magnetoresistive read element having a magnetoresistive film arranged between a pair of shields.
A magnetic writing apparatus has a medium for magnetically writing information thereon, a read-write head composed of a write element for writing the information on the medium and a read element for converting a change in a magnetic field leaking from the medium on which the information is written, a circuit for controlling input and output signals, a mechanism for rotating or moving the medium, and a positioning mechanism for determining a position of the read-write head relative to the medium. The write element comprises a coil for generating a magnetic flux, a pair of magnetic cores for collecting the magnetic flux, and a write gap for generating a magnetic field, the write gap being provided between the pair of magnetic cores. The operation of writing information is performed by applying the magnetic field, generated by conducting pulse shaped write current to the coil, onto the medium. The read element comprises a pair of shields made of a soft magnetic film, a magnetoresistive film arranged between the pair of shields and spaced a certain distance from each of the shields, and a pair of leads electrically connected to the magnetoresistive film. The magnetoresistive film can be roughly classified into an AMR film utilizing an anisotropic magnetoresistive effect and a GMR film utilizing a giant magnetoresistive effect. For example, a permalloy (Ni-Fe) film having a thickness of 5 to 30 nm is used as the AMR film. The electrical resistance of the AMR film is changed depending on the angle between the magnetization direction and the direction of the applied current. There is not a proportional relationship between the applied magnetic field and the electric resistance. Therefore, in order to improve the linearity between the applied magnetic field and an output signal, bias films are often laminated and arranged near the AMR film. The GMR film comprises a first ferromagnetic film having a thickness of 2 to 10 nm, the magnetization direction of which is changed by the magnetic field leaking from the medium, a second ferromagnetic film having a thickness of 1 to 5 nm, the magnetization direction of which is almost fixed, and a non-magnetic film having a thickness of 1 to 4 nm, which is inserted between the first ferromagnetic film and the second ferromagnetic film. The second ferromagnetic film and an antiferromagnetic film for fixing the magnetization of the second ferromagnetic film are often directly laminated. The electrical resistance of the GMR film is changed depending on an angle between the magnetization direction of the first ferromagnetic film and the magnetization direction of the second ferromagnetic film. In order to improve the linearity between the applied magnetic field and an output signal, the magnetization direction of the second ferromagnetic film is often set so as to be nearly perpendicular to an air bearing surface. The GMR film can obtain a higher output even with a small magnetic field as compared to the AMR film. That is, the GMR film is more sensitive, and accordingly it is advantageous for high density writing by a magnetic writing apparatus. In the magnetic writing apparatus, a change in the electrical resistance in the AMR film or the GMR film is detected as an output signal. The pair of shields are provided for detecting the change of the magnetic field leaking from the medium with a high resolution. As the shield-to-shield spacing is narrowed, the resolution becomes higher. Therefore, the shield-to-shield spacing is being narrowed corresponding to the future trend toward a higher writing density. A permalloy (Ni--Fe) film, a permalloy base Ni--Fe--Nb alloy film, a sendust (Fe--Al--Si) film, a Co base amorphous film and the like are used as the shield on a side of a substrate (a lower shield). Since the surface of the sendust film is large in roughness, but is hard, a part of the film is hardly pealed off and attached onto some other portions during a process of lapping the air bearing surface. Since the film surface of the amorphous film is flat, the amorphous film is advantageous in a case where the gap between the shields is narrow or in a case where the GMR film is used, which is very sensitive to the roughness of the substrate. As the other shield, that is, an upper shield, a permalloy (Ni--Fe) film is often used. In order to reduce a displaced width between a position of the write gap and a position of the magnetoresistive film used for reading in the read-write head described above, one of the pair of magnetic cores of the write element in the side near the read element, that is, the lower core, is also used as the upper shield of the read element in most cases.
In order to attain a high writing density in the magnetic writing apparatus, it is indispensable to make the best use of a read-write head of magnetoresistive effect type. However, the read-write head of magnetoresistive effect type sometimes causes an error in the magnetic writing apparatus by fluctuation in the reading waveform when a writing and reading operation is repeated. One of the causes of such a fluctuation in the reading waveform is an instability in the shield. The structure of the magnetic domain of the shield is changed every time there is a writing operation. As the structure of the magnetic domain of the shield is changed, the magnetizing state of the magnetoresistive film is changed to cause the reading waveform to fluctuate. One method of suppressing the fluctuation in the reading waveform has been proposed, for example, in U.S. Pat. No. 5,515,221, in which an anti-ferromagnetic film is laminated under a soft magnetic film composing a shield, and uniaxial anisotropy in a direction of the track width (a direction on an air bearing surface and normal to film thickness) is applied to the soft magnetic film.
In the proposal disclosed in U.S. Pat. No. 5,515,221, the manufacturing process becomes more complex compared to that of a conventional head because the soft magnetic film and the anti-ferromagnetic film are laminated. Further, in order to apply the uniaxial anisotropy to the soft magnetic film, it is required to anneal it at a high temperature of nearly 320 for about 10 hours. When the laminated film structure is applied particularly to the shield on the side near the write gap (the upper shield), the head often does not operate normally because the characteristics of the magnetoresistive film become deteriorated in the process of the heat treatment described above. Further, in a GMR head in which the above-mentioned laminated film structure is applied to the upper shield, the magnetization direction (directed perpendicular to the air bearing surface by the anti-ferromagnetic film) of the second ferromagnetic film composing the GMR film and the magnetization direction (directed toward the track width by the anti-ferromagnetic film) of the shield are in a nearly orthogonal relation to each other. Therefore, the precedently fixed magnetization direction of the second ferromagnetic film is sometimes moved in a following process for fixing the magnetization direction of the shield (a magnetic field is applied under a somewhat high temperature) to deteriorate the characteristics of the head. It is very difficult to fix the magnetization directions so that they are different from each other, as described above.
In a case where the shield on the side near the substrate is of a construction including the amorphous film, there sometimes occurs a noise called a noise-after-write or a popcorn noise within approximately 100 .mu.s after the writing operation. Since the film surface of the amorphous film is flat, the amorphous film is advantageous in a case where the gap between the shields is narrow or in a case where the GMR film is used, which is very sensitive to the roughness of the substrate. However, since the magnetic writing apparatus operates erroneously when the noise-after-write occurs, it is required to suppress the occurrence of such noise.